Latissimus dorsi

Below- the muscle attaches to the spinous processes of lowesix thoracic vertebrae and all lumbar vertebrae and through the lumbar aponeurocic to the sacrum and to the posterior part of the crest of the ilium. It also attaches to the thoraco lumbar fascia. Vertical fibres of the muscle are attached to the lower three or four ribs

The muscle twist to 180* around teres major muscle.
Above- the muscle attaches to the intertubercular (bicipital) groove of the humeras.

NERVE SUPPLY : Thoracodorsal nerve (C6, C7,C8)

ACTION:

The latissimus dorsi does extension of arm at the shoulder joint( chopping wood)
Adduction,assists in internal rotaion and depression of humerus. ( helps in crutch walking, overhead chinning).

SYNERGITIC ACTION:

With the scapula stabilised, the teres major and the latissimus dorsi are strongly synergistic in humeral extension, adduction,and medial rotation because of their com-mon attachment to the humerus. Through the glenohumeral joint, the latissimus dorsi can strongly influence positioning of the scapula/shoulder girdle.
Lats and pecoralis major act synergistically with subscapularis for internal rotation.

Clinical impimentation :

Optimum length of the lats is very critical as when it is tight, the back arches while overhead movements to compensate, this also thicompresses the posterior structures of the spinal column. This is the common cause of LBA in people performing repetitive over head movements (athlets).

According to shahrman, relative stiffness also creates above problem. If the abdominal muscles ( which prevents lumbar lordosis) are weak, while doing overhead movements the back arches even if lats are not tight, and this may happen even before reaching optimal length of lats while perfoming overhead movements.

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